Acquired immune responses to an intranasally introduced Cryptococcus neoformans infection will be studied using a murine model. Experiments are planned to demonstrate whether protection against this etiological agent can be passively transferred with sensitized T-lymphocytes or serum from C. neoformans infected mice. Since a preliminary experiment indicates T cells are capable of transferring protection in this disease, it is expected that the proposed investigations will confirm that cell-mediated immunity (CMI) is protective. The lymphoid cells responsible for passive transfer of delayed-type hypersensitivity (DTH) and protection will be further characterized according to their surface antigens, such as Lyt and Ia antigens. Induction and kinetics of the DTH and protective immune responses will be studied in an attempt (1) to learn more about the relationships of in vivo and in vitro assays for CMI and the level of protection against a C. neoformans infection, (2) to determine whether localized tissue immunity, such as in the lungs, plays a role in limiting the dissemination of the etiological agent, and (3) to ascertain whether the concentration of the cryptocci in the infecting dose effects the degree of DTH or protective responsiveness of the host.